Diagnosis and treatment of various pathologic conditions can be achieved by integrating multimodal imaging systems that furnish complementary information to improve patient management. The availability of highresolution tomography systems, fast computers, and reliable algorithms for image reconstruction has improved disease diagnosis and treatment management. As medical practice moves into the molecular era, the realization that no single imaging method can provide solutions to the complex information derived from mole-cular imaging has heightened interest in the use of multimodal imaging to harness the strengths of different imaging methods. Optical imaging (OI) promises to complement established imaging methods by imaging mo-lecular events with a wide variety of reporting strategies and high detection sensitivity. However, due to the in-tense scattering of light by tissue and the rapid decrease in resolution as a function of depth, OI in deep tissue is challenging. While much progress is being made to improve standalone OI, including advances in diffuse optical tomography (DOT) methods, combining OI with well-established imaging modalities provides many po-tential advantages and will likely be critical to further advance molecular OI methods for eventual human use. Because of the high sensitivity of both PET and OI methods and the compatibility of their imaging agents, we will incorporate PET to OI to fuse the imaging datasets with identical pharmacokinetics but different reporting strategies. In this proposal, we will (1) synthesize and radiolabel novel PET-OI monomolecular multimodal imaging agents (MOMIAs) labeled with near infrared dye and PET radioisotope;(2) characterize the MOMIAs by in vitro enzyme and other assays;(3) develop instrumentation for PET-OI co-registration;and (4) establish tumor re-sponse function by PET-OI.